1. Field of the Invention
The present invention relates to a ring network which is applied to a local area network (LAN) and, more particularly, to a ring network switching control device for automatically reconfiguring a network in the event of a transmission-line failure by use of a duplex transmission line.
2. Description of the Related Art
Local area networks (LANs), in which a plurality of communication nodes (communication control devices which accommodate terminals and the like) are linked together via a transmission line in the form of a ring, thus allowing data interchange among distributed terminals and computers have been used widely.
In general, an advantage of duplex transmission lines is that, even when a fault occurs in one of the transmission lines, another transmission line can be used to continue the data communication and thus a reliable system is obtained.
Also, by forming the duplex transmission lines as two loops for transmitting data in reverse directions, even when both of the two lines are cut, or when a fault occurs in a node, the data communication can be maintained at a minimum scale of the system through a loop back.
In such a ring network, where a transmission-line failure and a change of state occur in a node, the transmission line is reconfigured.
In addition to the above-mentioned duplex line technology, when the system is recovered, it is necessary to reset the loop back or to expand the loop back to the recovered position of the system.
Based on the above, the present invention provides a system which enables the formation of a loop back and the resetting of each node (including a supervisory node), to obtain a flexible system operation.
As arts related to the present invention, the following publications are known:
1. U.S. Pat. No. 4,542,496 disclosing a conventional loop back control technology;
2. Japanese Unexamined Patent Publication (Kokai) No. 57-92,495 disclosing a prior art to the technology disclosed in the above U.S. Pat. No. 4,542,496;
3. Japanese Unexamined Patent Publication (Kokai) No. 59-40,739 disclosing a loop back technology with a supervisory unit; and
4. Japanese Unexamined Patent Publication (Kokai) No. 59-57,544 disclosing a loop back control without a supervisory unit. The art disclosed in this document is an alternative to that of the above Japanese Unexamined Patent Publication (Kokai) No. 59-40,739.
In the above related art, the parent station receives control information representing the state of transmission line 3 from respective communication nodes at regular intervals for centralized control of the entire state of the network. In the event of a failure, the parent station decides its state and transmits control information to each of communication nodes to control its switches (not shown), thereby switching between the #1 and #2 systems of transmission line 3 or performing a loopback of transmission line 3 for reconfiguration of the network. That is, the child stations, operate subordinately as prompted by the parent station.
In the above related art, however, a complex control procedure involving several stages or steps is required between the parent station and respective communication nodes in order to modify the configuration of the network system. This will waste a lot of processing time and consequently prolong the interruption of communication.
In addition, if a failure should occur in the parent station itself, the entire operation of the network will be stopped.
To solve the above problems, U.S. Pat. No. 4,930,119 (which corresponds to Japanese unexamined Kokai Publication 1-164,141) discloses a prior art for performing a communication control autonomously by enabling respective communication node to use the control data. The present invention is directed to a further specific and concrete technology for performing an autonomous control.